纳米材料的四大效应(科普知识)

The four effects of Nano material (scientific knowledge)纳米材料的四大效应（科普知识）First, surface effectT he direct ratio exists between the surface area and diameter’s square of spherical particles, also exsits between its volume and cubic, soits specific surface area (surface area/volume) and is in inversely proportion to the diameter. With the diameter of particle becoming smaller, surface area will increases gradually, indicates the percentage of the surface atomic accounts for will dramatically increases. The surface effect of particle what the diameter is bigger than 0.1 microns could be ignored, when the size is less than 0.1 microns, the percentage of its surface atom will dramatically grows, even the sum of surface area of 1 g ultramicroparticles is 100 square meters, the surface effect will not be ignored at this time.The surface of ultramicroparticles is very different with the surface of the large object, if we take the television camera to the metal ultramicroparticles (diameter of 10 ^ 2 * 3 microns) by using the high-rate electron microscope, and you will found that the particles has no fixed form through the real-time observation , with the time’s changing,it will automatically forms into various shapes (such as cubic octahedron, ten surface body, with 20 ulrich, etc.),the body which is different from the general solid and liquid, is a quasi solid. under the radiation of electron beam of the electron microscope,the surface atomic looks like entering into the condition of "boiling",the unstability of particle structure could be seen when the size is bigger than 10 nanometer, then microparticle has the stable structure state.the surface of ultramicroparticles has high activity, the metal particles will be quickly oxidated and burnt in the air. We can use the surface coating or deliberately control the oxidation rate to prevent spontaneous combustion, make its slowly oxidated to generated a very thin and dens oxide layer to ensure the stabilizationof surface., because of the surface activity,the metal ultramicroparticles will become a new efficient catalyst ,gas storage materials and low melting point materialSecond, small size effectAs the quantitative chang of particles size, in certain conditions , the properties of particle would change in quality. particle size becomes smaller will be in order to macro physical characters changes ,we called this phenominon as small size effect. For Ultramicroparticles, Its size becomes smaller,and the surface area will dramatically increases at the same time,then produces the following a series of novel properties(1) The special properties of the optical: when gold was subdivided into the size that smaller than the wavelength of light wave, which means the gold loses their lusters of rich and honour and to be black. In fact, all of the metals are black in the state of ultramicroparticles.Size becomes smaller, the color is much more black, silver platinum (platinum) into platinum black, metallic chromium into chromium black.it shows the reflectivity of metal ultramicroparticles to the light is very low, usually less than l %, thickness of a few microns could completely extincts the light. Because of the property, it could be as converted materials with the high efficient sunlight and optoelectronics and other materials, could also change efficiently the solar energy into heat energy, electric power. In addition, it also may be applied in the infrared sensitive components, infrared stealth technology, etc.(2) when the size of solid matter what has special thermal properties becomes bigger, its melting point is fixed, we will find its melting point significantly reduce after being super fined, the phenominon is very remarkable especially when particles are less than 10 nanometer magnitude. For example, the conventional melting point of gold is 1064 C ℃, when the size of particle reduces to 10 nanometer, the temperature would lower 27℃, the melting point is 327 ℃when the size is 2 nanometer; the conventional melting point of Silve is 670 ℃, and the melting point of superfine silver particles could be lower than 100℃. Therefore, the Conductive slurry what is made of ultrafine silver could sinter at the low-temperature, at this time ,the substrate of components could only use plastic not the high-temperature ceramic materials, thestrengths of using superfine silver size could make the film to be averaged thickness, and the covering area is large, not only does saving materials but high quality. The company of Japan kawasaki steel uses 0.1~1 micron copper, nickel ultramicroparticles to make conductive slurry what can be replaced precious metals, for example, silver,palladium and so on. The nature of the dropping melting point of the ultramicroparticles has a certain attraction for the powder metallurgy industry .For example,adding ultrastructure nickel particles at the ratio 0.1% ~ 0.5% in weight into the tungsten particles,which could decreased the sintering temperature from 3000 ℃ to 1200~1300℃,so that we can fire into the high power substratee of semiconductor pip under the low temperature(3) People found the ultrastructure magnetic particles exsited in the organisms of the dove,dolphins,butterfly,bees and live in the water of magnetotactic bacterial,etc.because of the ultrastructure magnetic particles, this kind of biological could tell the direction under the magnetic field navigation,has the ability of return. The essence of magnetic ultramicroparticles is a biological magnetic compass,the magnetotactic bacteria what is living in the water relys on it ,and swam to rich nutrition near the bottom. The research through the electronic microscope shows that, the magnetic oxide particles in diameter with 2 '10-2 microns were contained in the body of magnetotactic bacteria. The ultrastructure magnetic particles with small size is significant different with the large material, the pure iron coercive force in large chunks is about 80 Ann/m, and when the particle size reduced to the below of 2 '10-2 microns, the coercive force can increase 1000 times, If further reduce its size, about less than 6'10-3 microns,the coercive force reduced to zero, presents Superparamagnetic. By using the characteristics of high coercive force of magnetic ultramicroparticles, the people has made the magnetic recording magnetic powder with the high storage density , what has widely applied to tape, disc, magnetic card and key,etc. taking the advantage of Superparamagnetic, people have already made magnetic ultramicroparticles into magnetic liquid what has extensive used in many fields.(4) the special character of mechanics: ceramic materials are brittle in the normal condition, but the nano ceramic material what was squelched by the nanometer particles has good toughness. Because the nanometer material with large interface, the atomic arrangement is quite chaotic in he interface, the atoms is easy to migration when the external force deformed, which shows good toughness and certain ductility,and makes ceramic materials with novel mechanical properties. American researchers reported the nanometer material could bend but not break in the room tenperature. Research shows the truth why people's teeth are with very high strength is that it is made of the materials just like calcium phosphate,etc, the hardness of the metal nanoparticles is higher than theraditional coarse grain metal by 3~5 times.As for composite nanomaterials, just like ceramic and metal, could change the mechanical properties in a wider range, and its application foreground is very broad. small size effect of Superfine particles still behaves in the superconductivity, dielectric properties, acoustic properties and chemical properties, etc.Third,the tunnel effect of macroscopic quantumThe atom of every kind of element has a specific spectra, such as sodium atom has yellow spectra. We have used the concept of energy to reasonally interpret the Atom model and the quantum mechanics, the energy of single atom would be combined into energy band when the countless atoms are made of solid, because the number of electronic is massive ,and the spacing of the energe level in energy band is small,so we can regard it as the state of continues. By using of the theory of the energy band ,we can successfully explain the relationship and difference between the large metal,semiconductor,and insulators. For the ultramicroparticles, what exsits in the middle of the atoms,molecules and the large solid, the continuous energy band of large materials will be split into dividable energy level; the Spacing of energy level would increases as the reduce of particle size decreases. A series of abnormal properties what are different from the macro object will appear When the spacing of heat energy, electric field or magnetic field is smaller than the average spacing, which we call quantum size effect. For example, the conductive metal can be changed into an insulator in the condition of ultramicroparticles, the distance of magnet is relevantwith the numble of electronic in the particles whether is oddnumble or even. specific heat will also take abnormal change, the spectra line would moves to the direction of the short wave long, this is macroscopic performance of the quantum size effect. Therefore, we must consider the quantum effect when the ultramicroparticles is at low temperature, the original macro regularity was no longer established. Electronic has the characteristic with volatility and particles, therefore, the tunnel effect exsits.In recent years, people found some macro physical quantities, such as the magnetized strength of microparticles, the magnetic flux of quantum coherent devices also shows the tunneling effect,which we called the macroscopic quantum tunnel effect. Quantum size effect,macroscopic quantum tunnel effect will be the foundation of future microelectronics, optoelectronic devices, or it established the limitation of existing microelectronics devices taking the further miniaturization,we must consider the above quantum effect when microelectronics devices taking the further miniaturization.For example,on the condition of manufacturing semiconductor integrated circuit, electronic would overflows device through the tunnel effect when the size of the circuit is close to electronic wavelength, make the device does not work properly, the limited size of classic circuit is about 0.25 microns.The development of quantum resonance tunnel transistors is a new generation devices what is made by using the quantum effect at the present time.Fouth, the effect of quantum sizeThe energy level of electronic what is near to the the energy level of the metal Fermi is from continues to dividable, and the energy gap of nano semiconductor particles grows wider, these phenomena are both called quantum size effect.。